Rhodes et al., U.S. Pat. No. 3,250,325, is exemplary of a type of heat exchange device to which the improvement disclosed herein is directed.
This type of heat exchange device, such as a radiator for an internal combustion engine, has a plurality of parallel tubular conduits which extend between vessels or receptacles commonly called headers and through which engine coolant fluid flows. In contact with these tubes are heat exchange elements or spacers which present additional surface area to air passing between the tubes to accelerate heat removal from the tube surfaces. As shown in U.S. Pat. No. 3,250,325, the heat exchange elements or spaces may take the form of corrugated metal strips positioned between and soldered to adjacent tubular conduits. Each corrugation or fold comprises a planar base member which is slitted with metal turned out of the plane of the planar base to form a plurality of louvers.
It has been the objective of the heat exchanger manufacturing industry to produce the most efficient fin design with the minimum amount of material thus achieving a reduction in fabrication cost for a given capacity heat exchange structure. For example, the present gage of fin material used in production radiators for automobiles is 0.0022 minimum.
U.S. Pat. No. 1,257,201, issued Feb. 19, 1918, to C. A. Eligh for "Method of Making Heat Radiating Fins" suggests that it is desirable, though not essential, that the edges of the fin strips be strengthened, which is preferably done by folding them over.
U.S. Pat. No. 3,191,418 to Arthur M. Modine, issued June 29, 1965 for "Method and Apparatus Forming Serpentine Fins" suggests that the thickness of each fin be varied from 0.0024 at the conduit attachment portions to 0.0015 at the center of the fin between the conduits.
Attempts to use even thinner materials in the production of vehicle radiators have not been successful in producing a fin assembly capable of withstanding high stress concentrations within the radiator core. As a result, the fins are subjected to stresses that cause buckling and consequent interference with air flow through the fins.
It is an object of the present invention to permit the use of fin material having a thickness of 0.001 to 0.0008 inches minimum by providing a hem flange located at the highest stress point of the fin assembly thus forming a support column preventing the fin element from buckling.